How soon after pmt does Apple ship devices?

How soon after pmt does Apple ship devices?

I am waiting for a 7 Plus that was estimated Oct4-10th for delivery but Apple just charged my credit card today and status now has been changed to "Preparing for Shipment". I thought I remembered in the past that they don't charge your credit card until it's almost ready to ship or maybe that's just projection on my part.
Does anyone know if this is an indication that my phone will be shipping soon?